Polypropylene resins are utilized as molding materials in various fields, including convenience goods, kitchenware, wrapping films, automotive parts, machine parts, electrical parts, etc. Practically, propylene resins are used in the form of compositions by adding thereto various compounding ingredients or additives, depending on performances required for individual products. In the fields of, e.g., automotive exterior parts, etc. that require mechanical strength, propylene resin compositions wherein elastomers, talc, etc. are formulated have been utilized.
In view of recent trends in large-sized, thin-wall automotive exterior parts and a simplified process for manufacturing parts, it is required for the polypropylene resins to have more improved mechanical and physical properties such as impact resistance, flexural modulus, etc., to hardly cause flow marks or weld marks and to have high flowability enabling to cope with paintless finish.
On the other hand, unity in design with the body part weighed heavily in automotive exterior parts. Such unity was achieved so far, either by blending polypropylene resins with various colorants and then molding the blend, or by painting molded articles in the same color as the body part. Taking into account the simplified manufacturing process and recyclability of materials, such a polypropylene resin composition that can deal with non-painting and shows an good visual appearance, has now been demanded.
In order to meet the demand for non-painting, there was proposed a technique of blending polypropylene resins with aluminum flakes frequently applied, e.g., to paints for body, thereby imparting a metallic appearance similar to metallic coatings. However, because of poor compatibility with polypropylene resins, aluminum flakes used for paints tend to separate from polypropylene resins and readily agglomerate during the processing of melt molding, which makes difficult to stably produce molded articles exhibiting a good metallic appearance. Especially in polypropylene resins having improved flowability to deal with large-sized, thin-wall automotive exterior parts, a tendency to cause separation and agglomeration of aluminum flakes is observed notably.